Method and apparatus for etching a gold metal layer using a titanium hardmask

ABSTRACT

Disclosed is an inventive method for etching a gold metallization in a plasma processing chamber. The method includes introducing a substrate having a gold layer and an overlying titanium hardmask layer into the plasma processing chamber. The hardmask is first etched using conventional etching techniques. Then a plasma is formed in the chamber from an oxidizing gas and an etching gas. The etching gas is preferably a hydrochloric acid containing gas which may contain a chlorine containing gas. In addition, N 2  may be provided. The plasma is then used to etch the gold layer through the titanium hardmask.

This application is a divisional of application Ser. No. 09/345,974,filed Jun. 30, 1999, now U.S. Pat. No. 6,306,312, the disclosure ofwhich is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates generally to semiconductor processing and,more particularly to methods for etching gold layers in an IC layerstack.

In semiconductor IC fabrication, devices such as component transistorsare formed on a semiconductor wafer or substrate, which is typicallymade of silicon. Metallic interconnect lines, which are etched from ametallization layer disposed above the substrate, are then employed tocouple the devices together to form a desired circuit. Most commonly,metallization layers are made from aluminum or aluminum alloys, butthere is increasing use of other metals such as copper and gold. Tofacilitate discussion, FIG. 1A illustrates a cross-sectional view of aprior art integrated circuit structure 100, representing the layersformed during the fabrication of a typical semiconductor IC having agold layer.

A substrate 102 forms a base for an integrated circuit structure 100. Agold layer 104 is shown formed over the surface of the substrate 102. Ahardmask layer 106 (typically an oxide layer) is disposed above the goldlayer 104, and an overlying photoresist layer 108 is formed over thehardmask layer 106.

The photoresist layer 108 represents a layer of conventional resistmaterial that may be patterned using patterned reticles and a stepperthat passes light (e.g., ultra-violet light) onto the surface of thephotoresist layer 108. The layers of the integrated circuit structure100 are readily recognizable to those skilled in the art and may beformed using any number of known deposition processes, includingchemical vapor deposition (CVD), plasma-enhanced chemical vapordeposition (PECVD), and physical vapor deposition (PVD) such assputtering.

To etch the hardmask layer, the photoresist layer 108 is patterned witha suitable photolithography technique, and subsequently the exposedhardmask layer is etched. FIG. 1B shows a cross-sectional view of theprior art integrated circuit structure 100 after etching the oxidehardmask layer 106 to form a hardmask for the underlying gold layer 104.

Conventionally, gold layers have been etched using a Cl₂ chemistry atelevated temperatures of about 200° C. At such high temperatures, anoxide hardmask must be employed because of the relatively high etch rateratio of gold to oxide and the low selectivity to organic photoresist.FIG. 1C shows a cross-sectional view of the prior art integrated circuitstructure 100 after etching the gold layer using a Cl₂ chemistry at anelevated temperature of about 200° C. The elevated temperature Cl₂ etchprovides a reasonable etch rate, however, profile control is severelylimited and special high temperature reactor configurations must beused.

Due to equipment design and process throughput, a lower temperature etchprocess is often used to etch metallization layers. However, at lowertemperatures a gold etch process using an oxide hardmask is notefficient. Thus, titanium hardmask layers are typically employed to etchmetallization layers at lower temperatures of about 70° C. FIG. 2A showsa cross-sectional view of a prior art integrated circuit structure 200,representing the layers formed during the low temperature fabrication ofa typical semiconductor IC having a gold layer, after etching a titaniumhardmask layer 202.

The integrated circuit structure 200 includes a substrate 202, a goldlayer 204 formed over the surface of the substrate 202, a titaniumhardmask layer 206 disposed above the gold layer 204, and an overlyingphotoresist mask 208 formed over the titanium hardmask layer 206. Asdiscussed above, the titanium hardmask layer 206 is patterned utilizingthe photoresist mask 208. However, at low temperatures the Chlorine in aconventional Cl₂ chemistry attacks the titanium hardmask at the sametime it etches the gold layer, resulting in poor selectivity between thegold layer 204 and the titanium hardmask layer 206. Thus, the titaniumhardmask is etched away before the gold layer plasma etch process isfinished, resulting in a damaged gold layer 204 after plasma etch, asshown in FIG. 2B.

In view of the forgoing, what is needed are improved methods andapparatuses for etching a gold layer utilizing a titanium hardmask.Further, there is a need for methods and apparatuses that allow etchingof a gold layer at conventional or near conventional lower electrodetemperatures.

SUMMARY OF THE INVENTION

The present invention fills these needs by providing a gold etchingchemistry that can be used at conventional or near conventionalelectrode temperatures and provides greatly improved mask selectivitywith respect to a titanium hardmask. In one embodiment, a method foranisotropically etching a gold layer through an aperture in a hardmaskis provided. A substrate is introduced into a processing chamber inpreparation for a gold etch. The substrate includes a gold layer, ahardmask layer containing titanium formed above the gold layer, and anoverlying photoresist mask disposed above the hardmask layer. Thehardmask layer is then etched through the photoresist mask to create ahardmask for the underlying gold layer. Finally, a plasma is createdwithin the processing chamber from an oxidizing gas and an etching gas.The etching gas is preferably a hydrochloric acid containing gas whichmay contain a chlorine containing gas. In addition, N₂ may also beprovided. The plasma is then used to etch the gold layer through thehardmask.

In another embodiment, a system for etching gold layers is provided. Thegold layer etch system includes a chamber receptive to a substratehaving a gold layer and an overlying hardmask containing titanium. Alsoincluded in the gold etch system is a gas inlet mechanism connecting anoxidizing gas and an etching gas source to the chamber. The etching gasis preferably a hydrochloric acid containing gas which may contain achlorine containing gas. In addition, N₂ may also be provided. Furtherincluded in the system is a pair of electrodes disposed within thechamber, and an RF generator coupled to the electrode pair so that aplasma is formed with the oxidizing gas and the etching gas which etchesexposed portions of the gold layer through the hardmask.

In yet a further embodiment of the present invention an integratedcircuit having a gold layer formed in a plasma processing chamber isdisclosed. In this embodiment, the substrate, from which the integratedcircuit is later formed, is introduced into a processing chamber. Thesubstrate includes an underlying gold layer, a hardmask layer containingtitanium, and an overlying photoresist mask formed above the hard masklayer. The hardmask layer is then etched through the photoresist mask tocreate a hardmask. Next, a plasma is created within the processingchamber from an oxidizing gas and an etching gas. The etching gas ispreferably a hydrochloric acid containing gas which may contain achlorine containing gas. N₂ may also be provided. The plasma is thenused to etch the gold layer through the hardmask. Finally, the substrateis further processed to form an integrated circuit.

Advantageously, the improved titanium hardmask selectivity of thepresent invention allows the etching of a gold layer at conventional ornear conventional lower temperatures, thus avoiding the need for specialhigh temperature reactor configurations. This and other advantages ofthe present invention will become apparent to those skilled in the artupon a reading of the following description and a study of the variousfigures of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention, together with further advantages thereof, may best beunderstood by reference to the following description taken inconjunction with the accompanying drawings in which:

FIG. 1A is an illustration showing a cross-sectional view of a prior artintegrated circuit structure including an oxide hardmask layer prior toplasma etch;

FIG. 1B is an illustration showing a cross-sectional view of the priorart integrated circuit structure after etching the oxide hardmask layer;

FIG. 1C is an illustration showing a cross-sectional view of the priorart integrated circuit structure after etching the gold layer using Cl₂at high plasma temperatures;

FIG. 2A is an illustration showing a cross-sectional view of a prior artintegrated circuit structure including a titanium hardmask layer priorto plasma etch;

FIG. 2B is an illustration showing a cross-sectional view of the priorart integrated circuit structure layer after etching the gold layerthrough the titanium hardmask layer using Cl₂;

FIG. 3A is an illustration showing a cross-sectional view of anintegrated circuit structure prior to plasma etch in accordance with apreferred embodiment of the present invention;

FIG. 3B is an illustration showing a cross-sectional view of theintegrated circuit structure after etching the hardmask layer inaccordance with a preferred embodiment of the present invention;

FIG. 3C is an illustration showing a cross-sectional view of theintegrated circuit structure after etching the gold layer in accordancewith a preferred embodiment of the present invention;

FIG. 4 is a flowchart showing a method for etching a gold layer inaccordance with one embodiment of the present invention;

FIG. 5 is a flowchart showing a method for etching a gold layer using anetching gas containing HCl in accordance with another embodiment of thepresent invention;

FIG. 6 is a flowchart showing a method for etching a gold layer using anetching gas containing HCL/Cl₂ in accordance with yet another embodimentof the present invention; and

FIG. 7 is an illustration showing a gold layer etching system inaccordance with one aspect of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A-1C and 2A-2B were described in terms of the prior art. Apreferred embodiment of the present invention will now be described withreference to FIGS. 3A-3C. In the following description, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be obvious, however, toone skilled in the art, that the present invention may be practicedwithout some or all of these specific details. In other instances, wellknown process steps have not been described in detail in order not tounnecessarily obscure the present invention.

FIG. 3A is an illustration showing a cross-sectional view of anintegrated circuit structure 300 prior to plasma etch in accordance withone embodiment of the present invention. At the bottom of the integratedcircuit structure 300, there is shown a substrate 302. A gold layer 304is shown formed over the surface of the substrate 300, and a hardmasklayer 306 is disposed above the gold layer 304. The hardmask layer 306preferably contains a titanium component, such as TiO₂, TiW, and TiN. Anoverlying photoresist layer 308 is then formed over the hardmask layer306.

As discussed above, the photoresist layer 308 represents a layer ofconventional resist material that may be patterned using patternedreticles and a stepper that passes ultra-violet rays, electron beams, orx-rays onto the surface of the photoresist layer 308. The layers of theintegrated circuit structure 300 are readily recognizable to thoseskilled in the art and may be formed using any number of knowndeposition processes, including chemical vapor deposition (CVD),plasma-enhanced chemical vapor deposition (PECVD), and physical vapordeposition (PVD) such as sputtering.

To etch the hardmask layer 306, the photoresist layer 308 is patternedwith a suitable photolithography technique, and subsequently the exposedhardmask layer is etched. FIG. 3B shows a cross-sectional view of theintegrated circuit structure 300 after etching the hardmask layer 306 toform a titanium hardmask for the underlying gold layer 304.

The present invention uses plasma having components derived from anoxidizing gas and an etching gas to etch the gold layer 304 through thetitanium hardmask 306. The etching gas utilized in the present inventionis preferably a hydrochloric acid containing gas which may contain achlorine containing gas. In addition, N₂ may optionally be added to theplasma, as well as an inert carrier gas. The plasma is used to etch thegold layer at a temperature preferably less than 200° C., and morepreferably less than 100° C., and most preferably no greater than about70° C.

In a plasma, the HCL reacts with the titanium to form the hardmask andis believed to form TiH₂, a relatively non-volitile hybrid. The TiH₂film greatly improves selectivity of Ti to Au. In addition, thechemistry of the present invention can be used at normal electrodeoperating temperatures of about 70° C. Finally the etching gas derivedfrom HCl will not of its own passivate gold but in the presence ofoxidizing passivation agents, such as O₂, provides a good etch of gold,as shown in FIG. 3C.

Referring next to FIG. 4, a method 400 for etching a gold layer inaccordance with one embodiment of the present invention will now bedescribed. In an initial operation 402, the substrate is prepared forthe etching process in a conventional pre-etch operation. The pre-etchoperation may include, for example, forming the gold, titanium, andphotoresist layers using any number of known deposition processes,including chemical vapor deposition (CVD), plasma-enhanced chemicalvapor deposition (PECVD), and physical vapor deposition (PVD) such assputtering.

In substrate placement operation 404, the substrate having a gold layer,a hardmask containing titanium disposed above the gold layer, and anoverlying photoresist layer, is introduced into a plasma processingchamber. The substrate placement operation may also include, clampingthe substrate onto a chuck, stabilizing the pressure within the plasmaprocessing chamber, and introducing helium cooling gas to the substratebackside to facilitate heat transfer between the substrate and thechuck.

Next, in operation 406, the hardmask layer is etched. The hardmask layercan be etched with a chlorine-boron containing gas mixture such asCl₂/BCl₃/N₂. As will be apparent to those skilled in the art, chlorinefrom the chlorine-boron containing gas reacts with the titanium in thetitanium containing hardmask layer during the etch process. The actualparameters for etching a titanium layer are well known to those skilledin the art. Having etched the hardmask layer, the substrate is thenready for the gold layer etch.

The method 400 continues with a gold layer etch operation 408. Afteretching the hardmask layer, a mixture of an oxidizing gas and an etchinggas is formed into a plasma to anisotropically etch the gold layerthrough an aperture in the hardmask. The etching gas is preferably ahydrochloric acid containing gas, such as HCl, but may contain achlorine containing gas, such as Cl₂. In addition, N₂ may optionally beadded to the plasma, as well as an inert carrier gas. The plasma is usedto etch the gold layer at a temperature preferably less than 200° C.,and more preferably less than 100° C., and most preferably at about 70°C.

To elaborate further, the HCL reacts with the titanium to form thehardmask and is believed to form TiH₂, a relatively non-volatile hybrid,during plasma etch. The TiH₂ film greatly improves the selectivity of Tito Au. In addition, the chemistry of the present invention can be usedat normal electrode operating temperatures of about 70° C.

Finally, in operation 410, the substrate undergoes additional post-etchprocessing operations which are conventional in nature. Thereafter, thefinished substrate may be cut into dies, which may then be made into ICchips. The resulting chips may then be incorporated in an electronicdevice, e.g., any of the well known commercial or consumer electronicdevices, including digital computers.

FIG. 5 illustrates the process operations 500 associated with etchingthe gold layer using an etching gas containing hydrochloric acid inaccordance with one aspect of the present invention. In operation 502,the gold layer is etched using HCl/O₂ and optionally N₂. As describedabove, the HCL reacts with the titanium to form the hardmask and isbelieved to form a non-volatile TiH₂ film during plasma etch. The TiH₂film greatly improves selectivity of Ti to Au, thus allowing for a highdegree of profile control during the etch process, since small oxygenadditions can be tailored for profile slope control and not for titaniummask etch stop. In addition, the HCl will not of its own passivate gold,but in the presence an oxidizing agent, such as the O₂, will form finelines in the gold layer.

FIG. 6 illustrates alternative process operations 600 associated withetching the gold layer using an etching gas containing hydrochloric acidand Cl₂ in accordance with another aspect of the present invention. Inoperation 602, the gold layer is etched using HCL/Cl₂/O₂ and optionallyN₂. As mentioned earlier, the HCL reacts with the titanium to form thehardmask and is believed to form a non-volatile TiH₂ film which greatlyimproves selectivity of Ti to Au.

Plasma etching systems as described above consist of several components.FIG. 7 is an illustration showing a gold layer etching system 700 inaccordance with yet another embodiment of the present invention. Thegold layer etching system 700 includes a chamber 702 receptive tosubstrate 712 provided with a gold layer to be etched and an overlyinghardmask having an aperture and containing titanium. Also included inthe system 700 is a gas inlet mechanism 704 connecting an oxidizing gasand an etching gas source 706 to the chamber 702, a pair of electrodes708 disposed within the chamber 702, and an RF generator 710 capacitivlycoupled to the electrodes 708. In some instances the upper electrode canbe omitted by grounding the RF generator 710 to the chamber 702, or byproviding inductive coupling to the chamber.

After the substrate 712 is prepared for the gold layer etch, it isplaced in the chamber 702. The gas inlet mechanism 704 is then used torelease into the chamber 702, the oxidizing gas and the etching gas fromthe gas source 706. The RF generator 710 is then used to create a plasma714 containing the oxidizing and etching gases in the chamber 702. TheHCL in the plasma reacts with the titanium in the hardmask and isbelieved to form a non-volatile TiH₂ film forming the hardmask whichgreatly improves the selectivity of Ti to Au, resulting in a high degreeof profile control during the etch process as described above. Inaddition, etching gas derived from HCl will not of its own passivategold but in the presence of oxidizing passivation agents, such as O₂,provides a good etch of gold.

Thereafter, the substrate undergoes additional post-etch processingoperations which are conventional in nature, and the finished substrateis then cut into dies, which may then be made into IC chips.

While this invention has been described in terms of several preferredembodiments, there are many alterations, permutations, and equivalentswhich fall within the scope of this invention. It should also be notedthat there are many alternative ways of implementing the methods andapparatuses of the present invention. It is therefore intended that thefollowing appended claims be interpreted as including all suchalterations, permutations, and equivalents as fall within the truespirit and scope of the present invention.

What is claimed is:
 1. An etch system for gold layers, comprising: achamber having a substrate disposed therein, the substrate beingprovided with a gold layer to be etched and an overlying hardmask havingan aperture, wherein said hardmask contains titanium; a gas inletmechanism connecting an oxidizing gas and an etching gas source to saidchamber, said etching gas source containing a gas comprisinghydrochloric acid; at least one electrode disposed within said chamber;and an RF generator coupled to said at least one electrode, whereby aplasma is formed with said oxidizing gas and said etching gas whichetches exposed portions of said gold layer through said hardmask.
 2. Asystem as recited in claim 1, wherein the etching gas further comprisesCl₂.
 3. A system as recited in claim 1, wherein the gas inlet mechanismfurther connects an N₂ gas source.
 4. A system as recited in claim 1,wherein the plasma is formed at a temperature no greater than about 200°C.
 5. A system as recited in claim 1, wherein the plasma is formed at atemperature no greater than about 100° C.
 6. A system as recited inclaim 1, wherein the plasma is formed at a temperature no greater thanabout 70° C.
 7. A system as recited in claim 1, wherein the hardmaskcontains TiO₂.